1. Field of the Invention
The present invention relates to an optical system for projection television having a large aperture ratio and a relatively wide field angle, more particularly the present invention provides improved resolution with uniform correction of aberrations across the entire projected image.
2. Description of the Prior Art
Recently in commercial establishments and also in home use, projection television has become more popular. Problems, however, have limited the acceptability of this form of entertainment because of the cost and image quality.
Reflecting optical systems have been widely employed for projecting the video image on a large display screen. These optical systems, however, have experienced many problems with regard to correction of aberrations that are generated by the magnification of the images. As noted in U.S. Pat. No. 4,073,574 both Schmidt systems and meniscus lens systems have been employed in efforts to correct aberrations resulting from reflecting optical systems. The Schmidt system attempts to correct the spherical aberration generated by a concave mirror by a so called Schmidt plate having an aspherical surface. The Schmidt system, however, has a disadvantage in that while it is capable of providing a complete aberration correction for a selected given point on the display screen, it still provides a residual aberration which increases with distance from that point, thus causing a considerable image degradation. As can be readily appreciated, since the field angle in these video optical systems are usually at least 40 degrees in width at a minimum, the Schmidt system results in inadequate sharpness in the zonial and marginal areas of the display screen.
The use of a meniscus lens system on the other hand permits a uniform aberration correction across the entire area of the screen, however, the overall degree of correction is fairly low and hence the result is not satisfactory.
The prior art is still attempting to provide improved image resolution at an economical cost to increase the market for projection television systems.